Accusations from an informer in the Real IRA that Irish police ignored a clear warning about the Omagh bomb massacre will be raised in the Commons this week. The claims from Real IRA double agent Paddy Dixon about the atrocity were revealed in The Observer last month.

A cross-party group of MPs has put down an Early Day Motion challenging Tony Blair's Government to press its Irish counterpart to hand over Dixon from the Garda to the Police Service of Northern Ireland. The PSNI inquiry team into Omagh has not been allowed to question Dixon.

The Labour, Tory and Liberal Democrat MPs are also calling for a public inquiry into the handling of intelligence and agents inside the Real IRA in the run-up to the 1998 bomb which killed 29 people and two unborn babies.

MP Harry Barnes, former Northern Ireland Minister Peter Bottomley, Ulster-born Liberal Democrat Lembit Opik and Labour MP Rudi Vis are demanding that the inquiry is held on both sides of the Irish border.

The MPs motion to be tabled in the Commons tomorrow states, 'that this House is deeply disturbed at accusations in a report by Henry McDonald in The Observer on 19 October 2003 that senior Irish police officers ignored a clear warning about the Omagh bomb atrocity to preserve Dixon's role in the terrorist organisation.'

Relatives of those killed on 15 August 1998 welcomed the MPs' intervention.

Victor Barker whose son James was killed in the car bomb explosion said: 'Pressure needs to be brought to bear continually both on Mr Blair and his counterpart Bertie Ahern. After The Observer's story last weekend I wrote to Mr Ahern and asked him to order the Garda to hand over Paddy Dixon to the PSNI. It's a week on and I haven't even got an acknowledgement from the Taoiseach's office about my letter.'

Barker, a Surrey based solicitor who moved from Ireland back to England following his son's murder, is also preparing to take a groundbreaking case to the European Court of Human Rights against the Irish State.

The Observer has obtained a 54-page transcript of a taped conversation between Dixon and his Garda handler Detective Sergeant John White. In the recording, Dixon warns the Irish State that 'Omagh is going to blow up in their faces'. The tape also includes Dixon's claim that 'they [the Real IRA] had got a car and they [the Garda] knew it was moving, they knew it was moving within 24 hours at that stage'.

During their conversation Dixon and White allege that a clandestine deal between the Irish government and the Real IRA just weeks after the massacre led to charges being dropped against eight men arrested after the bombing.